If they don't have to be edible, do they need to be real? Craft stores sell synthetic clays that can be baked in oven. You could make a plaster mold from a real coin, press said clay to the mold, gently remove it and bake. Castin resins would work as well.

Try buying real choclate coins and peel off the foil carefully, then use the foil as a mould to pour resin in. For each side. Glue the sides together, Then use this as a blank for a proper mould and you are then done. Cast your coins in resin with brown colouring.